#include<iostream> using namespace std; int main(){ int youku[125][156]={0},y,nn=0; cin>>y; for(int t=1;t<=y;t++){ for(int u=1;u<=y;u++){ cin>>youku[t][u]; if(t=u||t+u==y+1) nn+=youku[t][u]; } } cout<<nn; return 0; }